Mandel's experience as an elected official began as a Lyndhurst, Ohio city councilman, where he was elected in 2003. He served three years on the council's finance committee.

On January 24, 2005, Mandel sent a letter to Lyndhurst residents, proposing a one time tax rebate of $400, paying the postage for the letters from his campaign fund.[8][9] Faced with opposition from fellow council members, Mandel introduced and advocated for a 2 millproperty tax rollback, which would have saved the average homeowner $100 a year on a home valued at $160,000.[10] What passed council, on April 4, 2005, was a 1.5 mill rollback, which saved the average homeowner $75 a year.[11]

Mandel's first piece of legislation as a State Representative, H.B. 151, was an initiative to force the multibillion-dollar Ohio pension funds to divest from companies doing business in Iran. He joined State Representative Shannon Jones (R) in an attempt to make Ohio the first state in the nation to divest from Iran, but the legislation was never signed into law due to a compromise between state pension executives and Ohio House leadership, agreed to by Mandel.[14] Then Speaker of the Ohio House Jon Husted brokered a deal to drop half of the state's investments in Iran and Sudan with the eventual goal of removing all investment from the two countries.[15] In April 2010, Mandel appeared on CNBC's "Squawk on the Street" to discuss his leadership on Iran divestment in Ohio.[16]

In the 127th Assembly, Mandel, along with other members of the Ohio House who served in Iraq, were excused from voting on HB649 in December 2008, which provided payments to military veterans of the Middle East wars and compensation to families who had lost loved ones in the conflicts.[17][18]

In the 128th Assembly, Mandel was one of 19 house members to vote against HB108, a bill to make cockfighting a felony.[19] Mandel defended his vote by stating that he believed the General Assembly's time would be better spent focused on job creation, keeping people from leaving the state and returning fiscal responsibility to state government.[20]

Also in the 128th Assembly, Mandel voted against the Ohio House Bill 176,[21] the Equal Housing and Employment Act which "[p]rohibits discriminatory practices on the basis of "sexual orientation" and "gender identity" under many of the Ohio Civil Rights Commission (OCRC) Law's existing prohibitions against various unlawful discriminatory practices.".[22] The bill passed the Ohio House by a vote of 56 to 39.

In May 2009, Mandel announced his candidacy for Ohio Treasurer of State via web video.[23] Mandel's campaign generated controversy in late September 2010 when it ran a TV commercial falsely suggesting that Mandel's opponent, African-American Kevin Boyce, was a Muslim.[24] The commercial was criticized for playing on anti-Muslim bias,[24] and was ultimately withdrawn by the Mandel campaign.[25][26] However, voters subsequently received a campaign mailing with similar themes. The Mandel campaign said that the Ohio Republican Party was responsible for the mailers, which had already been sent bulk rate, up to a week prior.[27]

In October 2010, in response to an Ohio Democratic Party complaint, the Ohio Elections Commission found that Mandel had deceptively depicted Boyce (an African Methodist Episcopal) as a Muslim in the ads.[28][29] On November 2, 2010, Mandel was elected Ohio State Treasurer, defeating Boyce by 14 percentage points to become chief investment officer of state funds.[30]

During Mandel's time as treasurer, Ohio retained the highest possible rating from Standard & Poor’s for the state's $4 billion government investment fund.[31] On March 19, 2012, Mandel severed contracts with two major banks that handled $41 billion in Ohio pension investments, amid government investigations into whether the banks overcharged clients for currency trading accusing them of “systematically exploiting public pension funds and taxpayers.”[32]

Mandel was reelected to a second term as State Treasurer in 2014,[33] defeating Democratic State Representative Connie Pillich.[34]

Mandel was the Republican nominee to challenge Democratic Senator Sherrod Brown in the 2012 General Election.[35] Josh Mandel officially announced his candidacy for U.S. Senate March 1, 2012, in a speech to the Akron Press Club.[36] He won the March 6, 2012 Republican primary with 63% of the vote in a five candidate race.[37] In March, Mandel stated his reason for running: "I am running for the United States Senate because no longer can I stomach the gridlock and partisanship in Washington that has bankrupted Social Security, bankrupted Medicare, and caused one-half million jobs to leave Ohio in the past decade."[38]

Mandel's campaign was singled out by the independent fact-checking group Politifact for its "casual relationship with the truth" and its tendency to "double down" after inaccuracies were pointed out. The fact-checking group wrote: "For all the gifts Mandel has, from his compelling personal narrative as an Iraq war veteran to a well-oiled fundraising machine, whoppers are fast becoming a calling card of his candidacy."[43]

Mandel had raised $7.2 million through the first quarter of 2012; his $5.3 million cash on hand trailed Brown's $6.3 million.[44] Mandel benefited from massive support from conservative out-of-state superPACs, which raise unlimited amounts of money from anonymous donors. These outside groups, including Crossroads GPS, aired $10 million in TV advertising supporting Mandel and attacking Brown as of July 2012, outspending Democratically-aligned outside groups by more than five-to-one.[45] Mandel's campaign was aided by over $1 million spent primarily on attack ads by a 501(c)(4) organization called the "Government Integrity Fund".[46]

Mandel failed to unseat Sherrod Brown in the November 6, 2012 General Election, losing 45% to 51%.[47]

On August 27, 2013, Mandel was accused by his opponents of violating both federal and state campaign laws by using a vehicle owned by his U.S. Senate campaign for private use and/or business unrelated to the campaign. No charges were brought and there was no case made against him. Mandel was involved in a traffic accident with the vehicle on March 5, 2013 near Toledo, Ohio, nearly four months after the campaign.[48]

Mandel has called for the repeal of the Patient Protection and Affordable Care Act.[49] In a campaign advertisement during his 2012 Senatorial run, Mandel claimed opponent Sherrod Brown "cast the deciding vote on the government takeover of health care". Politifact has labeled as false the claim that Brown cast the deciding vote for the act. The description of the act as a government takeover of health care, by Mandel, has been labeled by Politifact as "nonsensical" and a "myth".[50]

Mandel has called for what he terms as "aggressive and responsible" energy exploration that protects "the air we breathe and water we drink" while reducing environmental regulation.[38] He supports the approval of the Keystone XL pipeline.[51] Mandel is a supporter of expanded coal plants and has criticized environmental groups for a so-called "war on coal."[52]

Mandel appeared on CNBC's Mad Money with Jim Cramer to discuss energy exploration. Mandel stated, "We call it the win-win-win. This is new job creation for the state of Ohio, this is affordable energy, bringing costs down for families throughout the state, senior citizens throughout the state, and its national security."[53]

Mandel has been an outspoken critic of scientific opinion on climate change. He has referred to climate change research as "riddled with fraud" and has vowed to fight attempts to advance clean-air standards.[52]

In October 2009, he appeared on the show Fox & Friends stating his support for listening to the military generals on the ground in Afghanistan.[54] In an interview at the Republican Jewish Coalition quarterly meeting in Ft. Lauderdale in 2009, Mandel said that under George W. Bush "we recognized the serious threat that America and worldwide democracies face from Muslim extremism." He credited the American military with achieving a turn around in the situation in Iraq.[55]

Mandel was a member of the American Israel Public Affairs Committee at The Ohio State University.[56] In 2008, he attended the 2008 AIPAC Policy Conference in Washington, D.C, where he gave an address, and was quoted as saying "It was inspiring, the young people so motivated and gung ho about strengthening the Israel-United States relationship... Israel is our best friend and ally in the Middle East and it’s important that we maintain a strong and lasting relationship with them."[56]

At this conference, Mandel stated Iran was a threat, and discussed his divestment initiatives as a legislator in Ohio.[57]

In February 2009, during Operation Cast Lead, the Israeli government issued a statement thanking Mandel for his support of the operation.[58]

Mandel and his wife Ilana reside in Beachwood, Ohio with their three children, Rosie, Judah, and Gideon. They were married August 28, 2008, in Jerusalem.[59]

Mandel said in a speech that his maternal grandfather, Joe, is originally from Poland and is a Holocaust survivor, while his maternal grandmother, Fernanda, is originally from Italy and was hidden from the Nazis by a Catholic family during World War II.[60] In a speech to the Republican Jewish Coalition, he said the tribulations of his grandparents and family inspired him to public service.[60]